Given that over 20% of the total U.S. electric energy production is consumed for lighting applications, significant savings can be made by the introduction of new, higher performance illumination sources. Such savings could be realized especially for any alternative light sources that provide improved energy efficiency as compared with the widely used, but very energy inefficient, incandescent light sources. For example, if the energy used for lighting in residential, commercial and industrial sectors could be reduced by as little as 5% in the U.S., over one billion dollars per year could be saved.
One alternate source of lighting is the inorganic Light Emitting Diodes (LEDs), as described in Overview of High Brightness LEDs and the Progress Towards High Power LED Illumination, Intertech conference, October 2001.
Attempts have been made to achieve white light sources with inorganic light emitting devices, as disclosed in U.S. Pat. No. 5,851,063 to Doughty et al.
Organic light emitting devices (OLEDs) are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic light emitting devices have the potential for cost advantages over inorganic LEDs. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. In addition, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants, while it may be more difficult to tune the inorganic emissive materials that are used in LEDs.
OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly popular technology for applications such as flat panel displays, illumination, and backlighting. OLED configurations include double heterostructure, single heterostructure, and single layer, and a wide variety of organic materials may be used to fabricate OLEDs. Representative OLED materials and configurations are described in U.S. Pat. Nos. 5,707,745, 5,703,436, 5,834,893, 5,844,363, 6,097,147, and 6,303,238, which are incorporated herein by reference in their entirety.
One or more transparent electrodes may be useful in an organic optoelectronic device. For example, OLED devices are generally intended to emit light through at least one of the electrodes. For OLEDs from which the light emission is only out of the bottom of the device, that is, only through the substrate side of the device, a transparent anode material, such as indium tin oxide (ITO), may be used as the bottom electrode. Since the top electrode of such a device does not need to be transparent, such a top electrode, which is typically a cathode, may be comprised of a thick and reflective metal layer having a high electrical conductivity. In contrast, for transparent or top-emitting OLEDs, a transparent cathode such as disclosed in U.S. Pat. Nos. 5,703,436 and 5,707,745 may be used. As distinct from a bottom-emitting OLED, a top-emitting OLED is one which may have an opaque and/or reflective substrate, such that light is produced only out of the top of the device and not through the substrate. In addition, a fully transparent OLED that may emit from both the top and the bottom.
As used herein, the term “organic material” includes polymers as wells as small molecule organic materials that may be used to fabricate organic optoelectronic devices. Polymers are organic materials that include a chain of repeating structural units. Small molecule organic materials may include substantially all other organic materials.